U.S. Pat. No. 3,684,186 issued Aug. 16, 1972, to William F. Helmrich discloses in FIG. 2 a known airblast fuel injector for gas turbine engines wherein the injector has generally concentric chambers for inner and outer air flows and intermediate fuel flow and generally concentric discharge orifices for discharging and intermixing inner and outer air flows and the fuel flow. U.S. Pat. No. 3,980,233 issued Sep. 14, 1976, to Harold C. Simmons illustrates an airblast fuel injector of similar construction for a gas turbine engine. Because of the typical low pressure drop of a prior art airblast type injector, such airblast injector has employed a fuel metering valve in a housing on the opposite end of an injector support strut considerably upstream from the injector tip and outside the combustor case to compensate for pressure head effects and provide adequate fuel distribution to the engine combustor. As a result, fuel back pressure is maintained only to a valve which is considerably upstream from the injector tip. The low fuel back pressure at the airblast injector tip, actually from the remote upstream fuel valve to the injector tip, makes the fuel downstream of the valve prone to vaporization when fuel temperature increases as explained in the next paragraph. In addition, the fuel passages downstream from the metering valve to the injector tip are circuitous and often small in size, being prone to vapor lock with adverse consequences as will be explained in the next paragraph.
As mentioned in U.S. Pat. No. 4,754,922, there has been an effort to increase the power (thrust) and efficiency of gas turbine engines especially for military use by raising operating temperature of the hot gas generated in the combustor for subsequent flow to the turbine and past the engine outlet. Although airblast fuel injectors of the type shown in FIG. 2 of the Helmrich U.S. Pat. No. 3,684,186 have performed satisfactorily in the current gas turbine engine where fuel temperature is about 250.degree. F. at the injector tip, initial tests of the same fuel injectors in higher temperature engines where fuel temperature at the injector tip is within the range of 300.degree. F. to 400.degree. F. have evidenced a problem of fuel vaporization in the fuel passages downstream from the fuel metering valve and at the injector tip from the higher temperatures involved. The fuel vaporization results in vapor lock condition in the fuel passages causing pulsing or intermittent interruptions in fuel flow from the injector which in turn causes combustion instability and adversely affects operation of the engine.
Aforementioned U.S. Pat. No. 4,754,922 describes an airblast fuel injector and method for reducing fuel vaporization in an airblast fuel injector tip by positioning a cantilever spring fuel metering valve at an upstream axial location relative to the fuel discharge orifice to reduce fuel vaporization upstream of the valve location and yet provide for formation of a fuel stream amenable to the airblast effect of the inner air stream such that the airblast operational characteristics of the injector are not adversely affected.
U.S. Pat. No. 3,598,321 issued Aug. 10, 1971, to Darrel G. Bobzin illustrates a fuel injector construction for a gas turbine engine having multiple rectilinear leaf spring valves carried on a cylindrical valve plate with each leaf spring valve received in a chordal type slot in the valve plate for controlling fuel flow between cylindrical passages extending from the outer periphery to an inner cylindrical bore in the valve plate. However, the fuel injector disclosed is not an airblast fuel injector and is not exposed to higher fuel temperatures associated with recently developed engines.
U.S. Pat. No. 2,107,998 issued Feb. 8, 1938, to E. A. Rullison describes an air valve carburation device wherein a flexible annular reed valve is held on a supporting disk and against a valve seat to control air flow to an engine and is opened by a vacuum condition in the carburetor.